The present invention relates to a method of producing a lithographic printing plate which is excellent in press life, without undergoing development processing. More particularly, it relates to a method of producing a lithographic printing plate wherein plate-making is conducted by heat mode image recording, the image recording can be carried out scanning exposure based on digital signals, development processing is eliminated, the plate-making is performed on a printing machine and followed by printing as it is, and the resulting printing plate is reusable.
Among various printing methods, a lithographic printing method, particularly, an offset printing method has been conventionally employed and is, at present, one of the main printing methods since a manufacturing process of a printing plate used therefor is simple. The offset printing technique is based on the incompatibility of oil and water. An oily material, i.e., ink, is selectively retained in an image area and dampening water is selectively retained in a non-image area. By bringing an ink carrying-printing plate into contact with a material to be printed directly or indirectly via an intermediate which is called a blanket, the ink on the image area is transferred to the material to be printed, thereby conducting the printing.
In the offset printing method, a PS plate comprising an aluminum substrate as a support having coated thereon a diazo photosensitive layer is mainly used. The aluminum support of a PS plate is subjected to surface-graining, anodizing or other various treatments to promote the ink receptivity of the image area and ink repellency of the non-image area. Thus, a printing plate obtained can have an accurate image on the substrate and exhibit improved press life. Accordingly, the offset printing method is provided with good press life and highly accurate image in addition to simplicity.
However, further simplification of the offset printing method has been required with the prevalence of printed matter and a variety of simple printing methods have been proposed.
A typical example is a printing method including a method of manufacturing a printing plate by means of a silver salt diffusion transfer process as described, for example, in U.S. U.S. Pat. No. 3,511,656 and JP-A-7-56351 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). Such a type of printing plate is also commercially available from Agfa-Gevaert N.V. as Copyrapid offset printing plate. According to the method, a transfer image which is oleophilic can be formed through one step and can be used as a printing plate as it is. Thus, the method is practically used as a simple printing method. Although the method is simple, it still includes a diffusion transfer development step with an alkaline developing solution. Therefore, a simpler printing method which dose not contain a development step with a developing solution has been demanded.
Under such circumstances, various investigations to provide a simple method of manufacturing a printing plate without performing a development step with an alkaline developing solution after imagewise exposure has been made. Such a type of printing plate is called a processless printing plate in the field of a simple printing plate since a development step can be eliminated. Many methods based on various principles, for example, (1) image formation by thermal destruction of an irradiated part on an image recording surface by imagewise exposure, (2) image formation by oleophilization due to heat mode curing of an irradiated part by imagewise exposure, (3) image formation by oleophilization due to light mode curing of an irradiated part by imagewise exposure, (4) change of surface property by photolysis of a diazo compound, and (5) heat transfer of an image area by heat mode melting have been proposed.
The simple offset printing methods described above include techniques described, for example, in U.S. Pat. Nos. 3,506,779, 3,549,733, 3,574,657, 3,739,033, 3,832,948, 3,945,318, 3,962,513, 3,964,389, 4,034,183, 4,081,572, 4,693,958, 4,731,317, 5,238,778, 5,353,705, 5,385,092, 5,395,729 and European Patent 1,068.
Although these techniques do not need a developing solution at plate-making, they have at least one of the drawbacks in that the difference between an oleophilic area and a hydrophilic area is insufficient, consequently an image quality of a printed image is inferior, in that a resolving power is poor, consequently a printed image having excellent sharpness can hardly be obtained, in that an image portion is insufficient in mechanical strength and is liable to be damaged, resulting in the necessity of providing a protective film, consequently the simplicity is rather lost, and in that the durability capable of enduring long term printing is insufficient. These facts show that only the elimination of an alkaline developing step does not lead to the solution of the problem. Therefore, a method for making a printing plate which fulfills characteristics required for printing and can easily produce a printing plate has been strongly desired. However, such a method has not been realized yet.
Another method of producing a processless printing plate is a method utilizing zirconia ceramic which is rendered hydrophilic upon irradiation with light as described in JP-A-9-169098. However, since the zirconia ceramic has a low photosensitivity and the light conversion effect from hydrophobicity to hydrophilicity is insufficient, discrimination of an image area from a non-image area is unsatisfactory.
In addition to the simple plate-making method which does not use a developing solution as described above, development of means for treating a printing plate used to reclaim a printing plate precursor and reuse is advantageous to decrease in cost and reduction of waste matters. In order to reclaim and reuse a printing plate precursor, simplicity of operation for the reclamation is important in view of practical use. However, since development of the simple operation for the reclamation is accompanied with various difficulties, it has been hardly given serious consideration, and only such a method is proposed with respect to a special material for a printing plate precursor which is called zirconia ceramic in JP-A-9-169098 as described above.
Therefore, an object of the present invention is to solve the problems on heat mode plate-making process described above and to achieve improvements in characteristics.
Specifically, an object of the present invention is to provide a method of producing a lithographic printing plate of heat mode type wherein development processing is not demanded, the plate-making is simple, a printing plate precursor can be directly mounted on a printing machine for the plate-making, and a printing plate which is excellent in press life and provides printed matter of less stain is produced.
Another object of the present invention is to provide a method of producing a lithographic printing plate of heat mode type wherein the plate-making is easily conducted by a scanning image exposure system using a laser beam and a printing plate having excellent discrimination of an image area from a non-image area.
A further object of the present invention is to provide a method of producing a lithographic printing plate which can be reclaimed and used repeatedly.
Other objects of the present invention will become apparent from the following description.
The present inventors found that when a metallic compound layer which has a photo-catalytic property and a hydrophilic surface and bears light-heat convertible minute particles on the surface thereof is subjected to irradiation of heat mode such as an infrared ray, an ink-receptive region (hydrophobic region) is formed by the action of heat received and the ink-receptive region (hydrophobic region) returns to the inherent hydrophilic region by irradiation with an active ray having a short wavelength, and as a result of extensive investigations they completed the present invention.
The present invention includes the following methods:
1. a method of producing a lithographic printing plate which comprises subjecting a printing plate precursor comprising a support having a metallic compound layer which has a photo-catalytic property and a hydrophilic surface and bears light-heat convertible minute particles on the surface thereof to imagewise irradiation of heat mode to convert polarity of the metallic compound layer, thereby forming an imagewise hydrophobic region,
2. the method of producing a lithographic printing plate as described in item 1 above, wherein the metallic compound layer which has a photo-catalytic property and a hydrophilic surface and bears light-heat convertible minute particles on the surface thereof is one formed by irradiating a metallic compound layer having a photo-catalytic property with an active ray in the presence of a water soluble salt of metal which constitutes the light-heat convertible minute particles,
3. the method of producing a lithographic printing plate as described in item 1 or 2 above, wherein a covering rate of the light-heat convertible minute particles born on the surface of the metallic compound layer which has a photo-catalytic property and a hydrophilic surface is in a range of from 0.01 to 10% of the surface of the metallic compound layer,
4. the method of producing a lithographic printing plate as described in any one of items 1 to 3 above, wherein the printing plate precursor is one formed by removing printing ink from a lithographic printing plate produced according to the method as described in any one of items 1 to 3 above after conducting printing, and then subjecting the metallic compound layer of the lithographic printing plate to overall irradiation with an active ray, thereby rendering the surface of the metallic compound layer hydrophilic, and
5. the method of producing a lithographic printing plate as described in any one of items 1 to 3 above, wherein the printing plate precursor is one formed by removing printing ink from a lithographic printing plate produced according to the method as described in any one of items 1 to 3 above after conducting printing, and then subjecting the metallic compound layer of the lithographic printing plate to heating at the high temperature generating hydrophilicity, thereby rendering the surface of the metallic compound layer hydrophilic.